#include <HCSR04.h> // arduino library for ultrasonic sensor

#include <TimerOne.h>// arduino library for PWM functions

byte triggerPin = 12; // initializing pin 12 as the trigger pin of the ultrasonic sensor

byte echoPin = 13;// initializing pin 13 as the echo pin of the ultrasonic sensor

float t; // initializing variable that will store the frequency

int volume = 0; // initializing variable to store analog inputs of potentiometer that contols volume

int IR = 0; // initializing variable for IR sensor

int d = 0; // initializing variable to store duty cycle value

void setup () {

  Serial.begin(9600); // serial monitor to check output

  pinMode(9,OUTPUT); // setting buzzer pin as output

  HCSR04.begin(triggerPin, echoPin); // add variables to function argument

}

void loop () {

  double* distances = HCSR04.measureDistanceCm(); // storing the measurments into variable distances

  IR = analogRead(A1); // reading IR sensor and storing in val

  volume = analogRead(A2); // reading volume potentiometer value

  delay(10); // 10ms delay

  if (100 > distances[0] && IR<900){ // buzzer is only active if distance is less than 100cm & if the IR sensor's analog input is below 900, which indicates something is near

    t = 1000000/((10 - (distances[0]/10) ) + 1) ; // sets the frequency of the buzzer, it changes with the distance, and ranges from 1Hz to 11Hz

    d = map(volume,89,933,50,512); // mapping potentiometer values to fit in the desired range of the duty cycle (5% to 50%)

    Timer1.initialize(t);// setting frequency

    Timer1.pwm(9,d); // setting duty cycle

  }

  else{

      Timer1.pwm(9,0);; // turning buzzer off when the distance is greater than 100

  }

}